After Dr. Evil has pushed the Moon around the earth in his demonstration, he retrieves it and lines it up with Washington DC. The scene cuts to a full view of him. The canon on the moon is now firing way over the top of the earth.

Also, when he says that he'll fire in six hours, right after that he says, "Prepare the 'laser'!" It must take a while to start up, it needs six hours? And when Austin and Felicity go to the moon, shouldn't it take three days? Yet he gets there in time to stop Dr. Evil.